The Waterloo and City Line is a short underground railway line in London, built in 1898. It has only two stations, Waterloo and Bank, between which it passes under the River Thames. It exists almost exclusively to transport commuters arriving at Waterloo mainline station to the financial district of the City of London (and vice versa), and does not operate on Saturday evenings or Sundays.

It is colloquially known as The Drain. There are two main reasons for this: the smell of the marshy ground on which Waterloo is built, and the drain-like round deep-level tunnels, which were nicknamed "tubes" on the other lines.

In 2003 the Waterloo and City was closed for over three weeks for safety checks due to the derailment on the Central Line, which uses the same type of train.